Organic photoconductive layer sensitized with trimethine compound

ABSTRACT

WHEREIN R1 is hydrogen or phenyl; R2 is hydrogen, phenyl, 4-methoxyphenyl, naphthyl, 2-METHOXYNAPHTHYL (1) OR 4-METHOXYNAPHTHYL (1); R3 is hydrogen, methoxy, nitro or phenyl; R4 is hydrogen or methoxy; X is oxygen or sulfur atom; AND Y is perchlorate.   The present invention relates to organic photoconductive layers responsive to long wavelengths comprising a combination of an organic photoconductor and a sensitizer having the following chemical formula.

United States Patent 1191 Murakami et al.

1451 May 6,1975

[751 Inventors: Yoshinobu Murakami, Kalano;

Kazuhisa Morimnto. Settsu. both of Osaka. Japan [73] Assignee: Malsushita Electric Industrial Co.,

Ltd.

122] Filed: Aug. 23, 1972 I21 I Appl. No.: 282,970 [301 Foreign Application Priority Data Aug. 25. 1971 Japan 46-653l8 ()et. 4, 1971 Japan 46-78075 I52] U.S. Cl 96/l.6; 96/15 C; 260/240 R [51 Int. Cl G031: 5/06 158] Field of Search 96/16, 1.5, 1.7; 252/501 I56] References Cited UNITED STATES PATENTS 3,526,502 9/1970 Murakami el al. 96/16 X 3.567.438 3/1971 Hrooker et al..... 96/16 3,536,500 6/1971 Contais el al 9611.6 3,617,268 11/1971 Murakami et a1. 96/l.6 X 3,679,406 7/1972 Kryman 96/I.6 3.712311 1/1973 Murakami et a1. 96/1 .6

FOREIGN PATENTS OR APPLICATIONS 4420196 8/1969 Japan 96/16 45-4159 2/1970 Japan 96/16 lOO TRANSMITTANCE tn O 10-6-70, published in 889 0.6. 1367 on 8-31-71. Def. Pub. No. T889,023.

Petropoulos, C. C. et al., Def. Pub. of S.N. 194,487 filed ll-17l, published in 900 00.1234 on 7-2- 5-72, Def. Pub. No. T900031.

Reynolds. G. A. et .11., Def. Pub. of S.N. 235,845 filed 3-17-72, published in 904 0.0. 277 on 11-21-72. Del. Pub. No. T904277.

Primary lixaminerNorman (i. Torchin Assistant ExaminerJohn R. Miller Attorney. Agent, or I-irmWenderoth. Lind 8L Ponack I 57 I ABSTRACT The present invention relates to organic photocondue tive layers responsive to long wavelengths comprising a combination of an organic photoconductor and a sensitizer having the following chemical formula.

12 T CH=CH"CH Y R R1 3 R3 R2 I R1 wherein R is hydrogen or phenyl;

R is hydrogen. phenyl. 4-methoxyphenyl, naphthyl, 2-methoxynaphthyl l or 4-mcthoxynaphthyl l R is hydrogen, methoxy, nitro or phenyl;

R is hydrogen or mcthoxy;

X is oxygen or sulfur atom;

and Y is perchlorate.

5 Claims, 9 Drawing Figures WAVE LENGTH (m u) PATENIEDMM 61975 SHEET 10? 3 WAVE LENGTH {m u) 600 700 WAVE LENGTH (Fm LL) FIG.2

5 6 m w w 3;; kzmmmnuokoxu 700 800 WAVE LENGTH (m u) FIGS PATENIEDIMY' B1915 TRANSMITTANCE /0) TRANSMITTANCE SHEEI 2 0F 3 400 500 600 700 800 900 WAVELENGTH {an u) F l G 3 WAVELENGTH (rm u) FATENIEUMM $19. 5

FIGS

FIG]

FIGB

SHEET 3 BF 3 WAVE LENGTH (m u) WAVE LENGTH (m u) WAVELENGTH (m u) WAVE LENGTH (m u) ORGANIC PI-IOTOCONDUCTIVE LAYER SENSITIZED WITH TRIMETHINE COMPOUND This invention relates to photoconductive layers and more particularly to photoconductive polymer layers containing as a novel sensitizer. a trimethine compound.

Many kinds of organic photoconductive polymer layers are well known in the electrophotographic art for making copies of documents. drawings. transparencies. etc. It is necessary for the electrophotographic art that the photoconductive layer has a high photoconductivity in the long wavelength region of the visible spectrum or the near infra-red wavelength region. Such a photoconductive layer makes it possible for the electrophotographic art to employ an inexpensive and convenient light source such as a tungsten filament lamp in a reduced exposure time.

Interest in organic photoconductor cells has increased in the field of electronics, computers. high speed data recording and detecting systems. The applications mentioned above require a highly sensitive and transparent organic photoconductor preferably an organic photoconductive film-forming polymer.

The well-known organic photoconductive polymers are poly-N-vinylcarbazole, halogenated poly-N- vinylcarbazole, polyacenaphthylene. polyvinylanthracene. etc. The layers containing these photoconductive polymers are non-conductors of electricity before exposure and become electrical conductors upon exposure. It is known that an addition of a so-called sensitizer can improve photoconductivity and spectrum characteristics of the above photoconductive polymer. Conventional sensitizers are dyestuff compounds. such as xanthene dyes, triazine dyes or acridine dyes, but the conventional sensitizers are not entirely satisfactory for improving the photoconductivity and the spectrum characteristics of the photoconductive polymer.

An object of the invention is to provide an organic photoconductive layer having a high photoconductivity.

Another object of the invention is to provide an organic photoconductive layer having sensitivity to the long wavelength region of the visible spectrum or to the near-infrared wavelength region.

Another object of the invention is to provide a preparation method of particularly effective new class sensitizers of organic photoconductor. said sensitizers having a trimethine structure containing a certain substituted benzopyrylium or benzothiapyrylium salt.

Another object of the invention is to provide a transparent photoconductive layer.

Still other objects will be apparent from the following specification and claims.

These and other objects are accomplished by the use of photoconductive film-forming compositions comprising a photoconductive polymer and a novel trimethine compound.

The invention is further explained in the following description with reference to the accompanying drawings.

FIG. I represents the absorption spectrum of 2-[3'- (3 -phenyl-4"-p methoxyphenyl-2"- benzothiapyranylidene) propenyl l-3-phen yl-4-pmethoxyphenylbenzothiapyrylium perchlorate in dichloroethanesolution.

FIG. 2 represents the absorption spectrum of poly-N- vinylcarbazole film (l microns in thickness) contain- 2 ing 0.2 mole percent of 2- [3'(3"-phenyl-4"-pmethoxyphenyl-Z "-benzothiapyranylidene) propenyl 3-phenyl-4-p-methoxyphenyl-benzothiapyrylium perchlorate.

FIG. 3 represents the absorption spectrum of poly-N- vinylcarbazole film l0 microns in thickness) containing 0.2 mole percent of 2-[3'-(3"-phenyl-2"- benzopyranylidene) propenyl]-3-phenylbenzopyrylium perchlorate.

FIG. 4 represents the absorption spectrum of poly-N- vinylcarbazole film (10 microns in thickness) containing 0.2 mole percent of 2-[3'- 3", 6"-diphenyl-4"- (4"'-methoxynaphthyl( l "'))-2"-benzothiapyranylidene propenyl] 3. 6-diphenyl-4-(4'- methoxynaphthyl l ')benzothiapyrylium perchlorate.

FIG. 5 represents the wedge spectrogram for an electrophotographic material coated with a solution containing l0 weight percent of brominated poly-N- vinylcarbazole sensitized with 0.04 weight percent of 2-[ 3 3 '-phenyl-4"-p-methoxyphenyl'2 benzothiapyranylidene) propenyl ]-3-phenyl-4-pmethoxyphenylbenzothiapyrylium perchlorate. the brominated poly-N-vinylcarbazole being dissolved in a mixed solvent of four weight parts of chlorobenzene and one weight part of dichloroethane.

FIG. 6 represents the wedge spectrogram for an electrophotographic material coated with a solution containing l0 weight percent of brominated poly-N- vinylcarbazole sensitized with 0.04 weight percent of 2-[3-(3", 6"-diphenyl-2"-benzopyranylidenel propenyll-3. o-diphenylbenzopyrylium perchlorate. the brominated poly-N-vinylcarbazole being dissolved in a mixed solvent of four weight parts of chlorobenzene and one weight part of dichloroethane. FIG. 7 represents the wedge spectrogram for an electrophotographic material coated with a solution containing 10 weight percent of brominated poly-N-vinylcarbazole sensitized with 0.04 weight percent of 2-[3'- 3". 6"- diphenyl-4"-(4' "-methoxynaphthyl 1 2 '-benzothiapyranylidene propenyl1-3, 6-diphenyl-4-t 4 methoxynaphthyk 1 'l) benzothiapyrylium perchlorate. the brominated poly-N-vinylcarbazole being dissolved in a mixed solvent of four weight parts of chloroben' zene and one weight part of dichloroethane.

FIG. 8 represents the wedge spectrogram for an electrophotographic material coated with a solution containing l0 weight percent of brominated poly-N- vinylcarbazole sensitized with 0.04 weight percent of 2-[3'-(3"-pltenyl-Z"-benzopyranylidene) propenyll-3- phenylbenzopyrylium perchlorate. the brominated poly-N-vinylcarbazole being dissolved in a mixed solvent of four weight parts of chlorobenzene and one weight part of dichloroethane.

FIG. 9 represents the spectral response of the photocurrent of the photoconductor cell (sandwich type cell) which is fabricated in the following; a transparent NESA conducting glass. a photoconductive polymer layer consisting of 0.2 mole percent of 2-[3'-(3"- phenyl-4"-p-methoxyphenyl-2"- benzothiapyranylidene )propenyl l-3-phenyl-4-pmethoxyphenylbenzothiapyrylium perchlorate in poly- N-vinylcarbazole of IO microns in thickness and a vacuum evaporated aluminum electrode of 0.3 cm area. The applied electric voltage to said sandwich cell is DC 20 volts and the xenon lamp is used as a light source.

The new sensitizer according to the present invention has the following chemical formula:

R, R woecwwm R; R1 R; R,

wherein In R is hydrogen or phenyl; R is hydrogen, phenyl or 4-methoxyphenyl. naph- Table l -Continued Com- Name of Com mnd thyl. 2 -methoxynaphthyl( l or 4 pound methoxynaphthyl( l l5 R ts hydrogen, methoxy, mtro r phenyl. henmpyryhum perchlorate R is hydrogen or methoxy; j. 2-methyl-ib-diphengl-4- 4'-methoxynaphth \l( '1 henvopyry ium perc lorate X -f g or b ulfur k. Z-methyl-4- 2'-methoxynaphthyl( I) benzopyrylium and Y is an anion radical such as perchlorate. perchlorate The compounds having the chemical formula above 70 g' 'gi mts gfi lfgtg i ga y p y mentioned are called trimethine compounds. m. g-methylill fi-diphenly':-4- 2'-methoxynaphthyl( l '1 The trim hine corn nds are r d f)|- Elllopyryrum perc urute luwing chezricul equagg: Prepd e by the n. 2-methyl-4-p-methoxyphenylhenzothiapyrylium perchlorate X at; 1%),

R, R1 R1 wherein o. l-meglhyl-3-phenyl-4-p-methoxyphenylhemothiapyrylium perc orate hydrogen Ur phenyl p. 2-methyl'3.fi-dipheny|-4-p-methoxyphenylbenzo- R hydrogen. phenyl. 4-methoxyphenyl. naphthyl. thiapyrylium perchlorate 7 q. 2-methyl-4- 4'-methoxynaphthyl( I benzothiapyrylium methoxynaphthyl( l or 4 methoxynaphthylt l 4s perchmme R ls hydrogen. methoxy. nttro or phenyl; r. imethfi'l-B-phfnflA- 4'i1rlnethoxynaphthylll'l enzot iapyrylum perc orate hydroge F s. 2-methyl-3.6-diphenyl-4- 4-methoxynaphth \l( 1 '1 15 oxygen or UT 31 henzothiapyrylium perchlorate and Y is an anion radical such as perchlorate. F P heflwlhiuvyrilium I It 2 th lb perchlorate Thus. Z-methylbenzopyry tum 5.1 or me y enzou zummuxynupmhyu thiapyrylium salt is allowed to react with alkyl orthoforgenmhhiuwpygyg ufi peirahlorate h h h I I a o v. met y-.. lp eny- ..-met oxynap t y( mate In acetic anhydrrde at 40 to I30 C, preferably at henmhiupyrylium pemhlmme 80 to l [0C. w. g-methylhenmpyrylium chloroferrute Representative examples of Z-methylbenzopyrylium "mmlmhdmhenl'henmpmmm salts and 2-methylbenzothiapyrylium salts are listed in Table Table 2 lists additional information on the absorption Table l maximum in dichloroethane and melting point of said salts listed in Table l.

Com- Name of Compound Table 2 pound a. Z-methyl-S-phenylhenzopyrylium perchlorate Compound Melting Point Absorption Maximum h. 2-methyl3-phcnyl-8-methoxybenzopyrylium perchlorate tCl in dichloroetharte (mptl cv 'l-methyl-J-phenyl-6-methoxyhenzopyryIium perchlorate d. Z-methyl-K-phenyl-b-nitrohenzopyrylium perchlorate u. 177 I79 585 e. Z-methyl-d-p-methoxyphenylhenzopyrylium perchlorate h. 219 22!) Still r. 2-methyl-3-phenylJ-p-methoxyphenylhen/opyrylium c. 206 21m 375 perchlorate d. I34 I27 580 2 methyl-3.6-diphenyl-4-methoxyphenylhenzopyrylium e. 129 l30 442 perchlorate 2-methyl-4- 4'-methoxynaphth vlt I) benzopyrylium g- 211 7 475 h. Zlll-2ll 529 perchlorate Iv lKl lX-l- 5H iv 2-methyl-3-phenyl-4- 4-methoxynuphthyll l l Table 4 Continued The following description will explain a practical method for making the trimethine compounds with reference to exemplary compounds. The details of the preparation of other compounds will be apparent to those skilled in the art from the preceding disclosure and the following illustrative examples of preparative methods for various compounds according to the invention:

l. 2-[3-(3"-phenyl-2"- benzopyranylidene)propenyll-3-phenylbenzopyrylium perchlorate (compound No. l l6 Grams of Z-methyl- 3-phenylbenzopyrylium perchlorate is dissolved in 200 milliliters of acetic anhydride to a solution. After adding 19 grams of ethyl orthoformate. the solution is stirred for 15 minutes at 100C. After cooling to room temperature, the solution is slowly poured into 2 liters of 10 percent perchloric acid to obtain a precipitate. The precipitate is filtered off. dried. washed with 300 milliliters of acetonitrile and dried again to obtain 7 grams of lustrous crystals having a melting point of 253 to 255C.

2. 2-[3'-(3"-phenyl-4"-p-methoxyphenyl-2"- benzothiapyranylidene)propenylI-3-phenyl-4-pmethoxyphenyl-benzothiapyrylium perchlorate (compound No. l5)

4.4 Grams of Z-methyl-3-phenyl-4-p-methoxyphenylbenzothiapyrylium perchlorate (melting point 212 to 213C) which is obtained by the Grignard reaction of 2-methyl-3-phenylbenzothiachromone and p methoxyphenyl magnesium bromide. are dissolved in 80 milliliters of acetic anhydride to obtain a solution. After adding 3.8 grams of ethyl orthoformate. the solution is stirred for minutes at 100C. After cooling to the room temperature. the solution is slowly poured into 400 milliliters of 10 percent perchloric acid to obtain a precipitate. The precipitate is filtered off. dried and reprecipitated with dichloroethane-ethyl ether to obtain 6 grams of fine crystals having a melting point of 176 to 179C.

it has been discovered according to the invention the compounds listed in Table 3 are sensitizers which can improve the photoconductivity and the spectrum characteristics of photoconductive polymers such as poly- N-vinylcarbazole. brominated poly-N-vinylcarbazole. polyacenaphthylene. etc. These polymers. except brominated poly-N-vinylcarbazole. are prepared by a per se well known method. The brominated poly-N- vinylcarbazole can be prepared by the following method: To the solution of grams of poly-N- vinylcarbazole in 450 milliliters of chlorobenzene. there are added 18.44 grams of N-bromosuccinimide and 0.173 gram of benzoyl peroxide. The mixture is 6 heated at C for 2 hours while being stirred thoroughly and is poured into methanol to obtain a white polymer. The polymer is dissolved in chlorobenzene and again poured into methanol for purification. The pure polymer thus obtained as a precipitate exhibits upon elementary analysis a halogen content of 29.87 weight percent which approximates the value calculated. i.e. 39.44 weight percent ofthe monobromo substituted product from poly-N-vinylcarbazole. This indicates that the polymer obtained is a monobromo substituted product. The degree of bromination varies from 50 mole percent to 200 mole percent according to reaction conditions.

The novel sensitizer comprising at least one compound from the group listed in Table 3 is dissolved in a suitable solvent. such as dichloroethane. methylene chloride. chloroform. or a combination thereof. and is added to the solution of the photoconductive polymer described above. The preferable amount of the sensitizer added is from 0.01 to 5.0 weight parts in connection with I00 weight parts of the photoconductive polymer. Advantageously. the amount thereof is from 0.1 to 2.0 weight parts in connection with weight parts of the photoconductive polymer.

For the preparation of the photoconductive layer. a said solution of the photoconductive polymer and the sensitizer in a suitable solvent is applied to the suitable support such as the electroconductive support in per se usual manner. for example. by spraying, by means of blade coating. by means of whirler coating. etc.. and then dried so as to produce a homogeneous transparent photoconductive layer on the support. Operable solvents are benzene. toluene. chlorobenzene. dioxane. methylene chloride. dichloroethane and combinations thereof. Said solution may be incorporated with suitable plasticizers and/or organic colloids for improving the flexibility and strength of the photoconductive polymer. Operable plasticizers are as follows: chlorinated diphenyl. dimethyl phthalate. diethyl phthalate and octyl phthalate. Operable organic colloids are as follows: natural and synthetic resin. phenol resin modified with rosin. polyvinyl acetal. polyvinyl butyral. polyvinyl cinnamate. polycarbonate resin. Operable materials for electroconductive supports may be made of any materials e.g. metal plate or glass plate having an electrically conductive coating. plastic plate or foil or film made of electrically conductive resin or coated with evaporated thin metal layer or covered with cuprous iodide conductive layer. The transparent support can produce a transparent photoconductive or electrophotographic plate. foil or film.

The reproduction of images by the electrophotographic method is carried out as follows: when the photoconductive layer has been charged by means of a corona discharge apparatus. the sensitized layer with the support is exposed to light under a master and is then dusted over in a per se known manner with a resin powder colored with carbon black. The image that now becomes visible can easily be wiped off. It can also be fixed by heating at about C. From positive masters. positive images characterized by good contrast are produced.

This invention is still further illustrated with references to the following illustrative examples.

EXAMPLE 1 l Gram of polyacenaphthylene and 0.6 gram of. as a plasticizer. chlorinated diphenyl (commercially available as Kanechlor). are dissolved in 8 milliliters of chlorobenzene. To the solution are added 0.5 milliliters of dichloroethane containing 0.006 gram of a sensitizer corresponding to compound number listed in Table 3. The solution is applied to an aluminum plate by means of whirler coating and is dried to form a layer of 7 microns in thickness. After said aluminum plate provided with the layer is charged negatively by means of corona discharge with a charging device maintained at approximately 6000 volts in the dark. it is placed under a positive master and exposed to a l00W tungsten lamp at an illumination of 50 lux. and the said plate is powdered over with a developer in a per se known manner. This developer consists of toner and carrier. The toner consists of low melting point polystyrene. colophony and carbon black. The toner is mixed with a carrier sub stance such that the toner becomes triboelectrically charged with a charge opposite to that produced on the plate. A positive image is produced and is fixed by slight heating. In Table 5, there are shown the sensitivity which is defined as a half-decay-exposure in luxsecond units. said half-decayexposure is the exposure to reduce a surface potential of the photoconductive layer to a half of the surface potential in the dark. The smaller half-decay-exposure represents a higher sensitivity.

l Gram of poly-N-vinylcarbazole. 0.5 gram of chlorinated diphenyl (commerically available as Kanechlor) and 0.006 gram of a sensitizer. corresponding to compound number listed in Table 3. are dissolved in I0 milliliters of dichloroethane to obtain a solution. The solution is applied to a polyester film (0.] mm in thickness) having a cuprous iodide transparent conductive layer by means of blade coating and is dried to form a layer of IO microns in thickness. An electrophotographic image is produced in the same way as that described in Example 1. In Table 6. there are shown the sensitivity as the half-decay exposure in lax-second units.

It is clear from Table 6 that the novel sensitizers improve the photoconductivity of poly-N-vinylcarbazole.

EXAMPLE 3 l Gram otbrominated poly-Nw'inylcarbazolc (monobromosubstituted product). 0.5 grams of polycarbon ate resin (commercially available as Panlite-C). 0.3 gram of chlorinated diphenyl (commercially available as Kanechlor") and 0.002 gram of sensitizer listed in Table 3 are dissolved in a mixed-solvent of 8 milliliters of chlorobenzene and 2 milliliters of dichloroethane. This solution is applied to a polyester film (0.l mm in thickness) having a cuprous iodide transparent conductive layer by means of a blade coating and dried to form a layer of l4 microns in thickness. On this support. an electrophotographic image is produced in the same way as that described in Example I. Table 7 shows the sensitivity as the half-decay exposure in lux-second units.

It is clear from Table 7 and FIGS. 5 to 8 that the novel sensitizers improve the photoconductivity and the spectrum characteristics of brominated poly-N- vinylcarbazole.

EXAMPLE 4 A dichloroethane solution containing poly-N- vinylcarbazole and a sensitizer listed in Table 3 is up plied to a glass plate having an electrically conducting layer (commercially available as NESA GLASS"and the solvent is evaporated to obtain a sensitized photoconductive layer of 10 microns in thickness of poly-N- vinylcarbazole. The concentration of the sensitizer in poly-N-vinylcarbazole is 0.2 mole percent.

HO. 2 to FIG. 4 show the illustrations of the absorption spectra of the sensitized photoconductive films.

Then. aluminum is evaporated onto the parallel face of the layer as electrode to obtain a photoconductor cell (sandwich type cell). Area of the aluminum electrode is 0.03cm The cell is illuminated by a light which has a peak at an absorption maximum of the sensitizer. The light is obtained from a xenon lamp with a saturated CuSO solution and a colored glass.

The photocurrent increases almost linearly with applied electric field up to ZXIO volt/cm. Photocurrent is proportional to the intensity of the light.

The spectral response of the photocurrent is measured in a range from 400mg. to lOOUmp. with the xenon lamp and the monochromator (Hitachi type EPU-ZA). FIG. 9 shows the illustration of the spectral response of the photoconductor cell.

The invention has been described in detail with particular reference to preferred embodiments thereof but it will he understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

What we claim is:

1. An organic photoconductive layer comprising a combination of an organic photoconductor and a sensitizer having the following chemical formulav r CH=CWCHm R R R1 R3 3 R1 I R1 conductor and 0.01 to 5.0 weight parts of a sensitizer.

2. An electrophotographic material comprising an electrically conductive support layer and photoconductive layer. the latter comprising a combination of photoconductive polymer and a sensitizer having the chemical formula according to claim 1, said combination comprisng l00 weight parts of an organic photoconductor and 0.0l to 5.0 weight parts of a sensitizer.

3. An electrophotographic material according to claim 2, wherein said photoconductive polymer is one member from the group consisting of poly-N- vinylcarbazole brominated poly-N-vinylcarbazole and polyacenaphthylene.

4. A transparent photoconductive layer comprising a combination of a photoconductive polymer and a sensitizer having the chemical formula according to claim 1, said combination comprising I00 weight parts of an organic photo conductor and 0.01 to 5.0 weight parts of a sensitizer.

5. A transparent photoconductive layer according to claim 4, wherein said photoconductive polymer is one member from the group consisting of poly-N- vinylcarbazole and brominated poly-N-vinylcarbazole. 

1. AN ORGANIC PHOTOCONDUCTIVE LAYER COMPRISING A COMBINATION OF AN ORGANIC PHOTOCONDUCTOR AND A SENSITIZER HAVING THE FOLLOWING CHEMICAL FORMULA. (=X-(4-R3,6-R4-1,2-PHENYLENE)-C(-R2)=C(-R1)-)>C-CH=CHCH=C<(-X-(4-R3,6-R4-1,2-PHENYLENE)-C(-R2)=C(-R1)-) (+) . Y(-) WHEREIN R1 IS HYDROGEN OR PHENYL, R2 IS HYDROGEN, PHENYL, 4-METHOXYPHENYL, NAPHTHYL, 2-METHOXYNAPHTHYL (1) OR 4-METHOXYNAPHTHYL (1), R3 IS HYDROGEN OR METHOXY, R4 IS HYDROGEN OR METHOXY, X IS OXYGEN OR SULFUR ATOM, AND Y- IS A PERCHLORATE RADICAL, SAID COMBINATION COMPRISING 100 WEIGHT PARTS OF AN ORGANIC PHOTOCONDUCTOR AND 0.01 TO 5.0 WEIGHT PARTS OF A SENSITIZER.
 2. An electrophotographic material comprising an electrically conductive support layer and photoconductive layer, the latter comprising a combination of photoconductive polymer and a sensitizer having the chemical formula according to claim 1, said combination comprisng 100 weight parts of an organic photoconductor and 0.01 to 5.0 weight parts of a sensitizer.
 3. An electrophotographic material according to claim 2, wherein said photoconductive polymer is one member from thE group consisting of poly-N-vinylcarbazole, brominated poly-N-vinylcarbazole and polyacenaphthylene.
 4. A transparent photoconductive layer comprising a combination of a photoconductive polymer and a sensitizer having the chemical formula according to claim 1, said combination comprising 100 weight parts of an organic photo conductor and 0.01 to 5.0 weight parts of a sensitizer.
 5. A transparent photoconductive layer according to claim 4, wherein said photoconductive polymer is one member from the group consisting of poly-N-vinylcarbazole and brominated poly-N-vinylcarbazole. 